Astronomers discover oldest galaxy yet seen

Galaxy is believed to have existed 480 million years after the Big Bang.

The Hubble Space Telescope's photo of a candidate galaxy (the zn in~10 galaxy) and the position on the Hubble Ultra Deep Field (HUDF) where it was found. The galaxy is touted as the oldest, most distant one yet seen by Hubble. This field
(Photo: Hubble Telescope/NASA)

Astronomers using the Hubble Space Telescope have peered further back in time than ever before, spotting a galaxy that formed less than 500 million years after the birth of our universe, making it the oldest and most distant ever seen.

The find, reported on Jan. 26 in the journal Nature, should help astronomers better understand the early days of the universe, researchers said. In particular, the discovery should shed light on the evolution of early galaxies, which first formed just a few hundred million years after the Big Bang.

"In essence, the most important aspect of this is, it provides us with some sense of how fast galaxies are building up," lead author Rychard Bouwens, of the University of California, Santa Cruz (UCSC) and Leiden University in The Netherlands, told SPACE.com. "It provides a sort of measuring stick."

The researchers found evidence of a galaxy with a redshift of 10.3. "Redshift" is a measure of how much the expansion of space has stretched an object's light to longer (or redder) wavelengths. Light from objects moving away from us shifts to the red end of the spectrum as its wavelengths are stretched. The shift, known as the Doppler phenomenon, is experienced on Earth when sound waves from an ambulance change pitch when the ambulance moves toward you versus away from you.

Astronomers use redshift measurements to determine an object's distance, and by extension its age. The bigger the redshift, the greater the distance.

A redshift of 10.3 corresponds to a distance of about 13.2 billion light-years. That is, it's taken 13.2 billion years for the light from the newly discovered galaxy — which has been named UDFj-39546284 — to reach us.

That makes UDFj-39546284 the most distant known galaxy in the universe, beating out the old record-holder by about 100 million light-years.

Since the universe is roughly 13.7 billion years old, UDFj-39546284 was around nearly at the beginning — just 480 million years after the Big Bang, or when the universe was just 4 percent of its current age.

Officially, UDFj-39546284 remains a "galaxy candidate," requiring some more observations to confirm its existence and age with certainty. But after performing a number of tests, Bouwens and his team are confident that the galaxy is there, and that its redshift is around 10.3.

"Everything we found was completely consistent with it being a real source," Bouwens said. "It looks really good right now."

Understanding galaxy formation

In addition to studying UDFj-39546284, the researchers also looked at several galaxies that are slightly younger, dating to about 650 million years after the Big Bang. They saw dramatic differences between the older and younger galaxies, suggesting that the rate of star birth jumped by a factor of 10 in the intervening 170 million years.

"This is an astonishing increase in such a short period, just 1 percent of the current age of the universe," co-author Garth Illingworth, of UCSC, said in a statement.

The team also found big differences in the number of galaxies observed in the two epochs. They discovered just the one galaxy dating to 480 million years after the Big Bang, while previous searches found nearly 50 galaxies just 170 million years later.

The new study also bears on an age-old question in astronomy. At about 300,000 years after the Big Bang, the hydrogen in the universe was neutral, meaning it carried no charge. By 1 billion years later, however, something had thrown off enough radiation to ionize most of this hydrogen, splitting it into its constituent electrons and protons.

"The results from this study imply that the stars and galaxies that they can detect would only provide about 12 percent of the radiation that you would need," Rachel Somerville of the Space Telescope Science Institute, who was not involved in the current study, told reporters on Jan. 26. "So this is quite a mystery that needs to be solved."

The new results hint that early galaxies such as UDFj-39546284 may have played a role in this reionization of the universe. But their contributions alone were perhaps not great enough to do the job, suggesting that some mystery source is also partly responsible, researchers said.

The team's observations in this regard are not definitive. To get to the bottom of the reionization mystery, astronomers will need to gather more data, according to Bouwens.

"At redshift 10, we made a relatively conservative assumption about how many of these faint galaxies there were," Bouwens said. "If there actually turn out to be more, they could be more important."

Looking to the future

While the new study takes an unprecedented look into the past, new instruments will likely be required to go back even farther, to the first epochs of galaxy formation, researchers said.

One of the most promising future instruments is NASA's James Webb Space Telescope (JWST), Bouwens said. The powerful successor to Hubble, JWST has long been hampered by cost overruns and delays.

Previously slated for launch in June 2014, JWST will be able to lift off no earlier than September 2015, according to an independent review panel convened last year to assess the telescope's problems.

Whenever it's finally cleared to take to the skies, JWST will have a huge impact, according to Bouwens.

"We're now just able to scratch the surface of what will be possible," he said. "We should be able to push out to redshift 12 or 13, and maybe further. It's unclear what we'll be able to do."